Trying to combine all my materials into one with my UV maps being seperate
I had the same issue, when exporting my model to unity. Here is how I handled it:


create a new UV-Map for every object. It's easier later if they all have the same name.
select all your objects in object mode and unwrap them. With the new created UV-Map selected for every object, all objects UV-Maps now should all be in the gray square of the UV-Editor.
Bake your textures from all the objects to a new image with the new UV-Map.


Hope this works for you :)